Approximately 6.2 million Americans have heart failure (HF) and the prevalence is increasing rapidly. HF is a common cause of hospitalization and mortality in older adults, and the cost of hospital care for HF is skyrocketing. One reason why HF is so burdensome and costly is that it is often complicated by cardiovascular and noncardiovascular comorbidities, especially in older patients. Psychiatric and medical disorders that are risk factors for incident HF persist after HF has developed, and additional comorbidities accumulate as patients with HF grow older. Thus, HF is embedded within a larger pattern of multimorbidity. Unfortunately, most trials of HF therapies as well as many other studies of HF have excluded patients with complex psychiatric and medical comorbidities or severe cognitive impairment. This has left large gaps in research on the care of older adults with HF. In addition, research on socioeconomic risk factors and health disparities has not been integrated with research on multimorbidity in HF. Heart failure is only one of multiple challenges facing patients with multimorbidity, stressful socioeconomic circumstances, and psychosocial problems, but the fragmentation of research on HF has left us with little understanding of patients with complex psychosocial problems. The purpose of this study is to identify combinations of comorbidities and health disparities may affect HF outcomes and require different mixtures of medical, psychological, and social services to address. It will encompass both psychiatric and medical comorbidities but will emphasize the role of psychiatric comorbidities. Syndemics theory is a useful framework for studying this type of psychosocial and medical complexity. Syndemics, also known as synergistic epidemics, occur when there are adverse interactions between prevalent disorders that concentrate in populations that are vulnerable due to adverse socioeconomic or environmental conditions. The syndemics framework has yielded important insights into a number of other disorders, but it has not been used to study the complex psychosocial problems of patients with HF. To our knowledge, this will be the first study of the syndemics of psychiatric and medical comorbidities in heart failure. The multimorbidity framework is an alternative approach for investigating the effects of multiple comorbidities on health outcomes. The specific aims of the study are: 1) to determine the coprevalence of major psychiatric and medical comorbidities in hospitalized patients with HF (n=535); 2) to determine whether coprevalent comorbidities have synergistic effects on 30-day all-cause readmission and mortality risks, heart failure self-care, and health-related quality of life; 3) to identify vulnerable subpopulations of hospitalized patients with HF who have higher coprevalences of syndemic comorbidities compared to less vulnerable subpopulations; 4) to determine the extent to which syndemic comorbidities explain adverse HF outcomes (30-day readmissions and mortality, poor self-care, and poor health-related quality of life) in vulnerable subgroups of hospitalized patients with HF; and 5) to determine the effects of multimorbidity on readmissions, mortality risk, self-care, and quality of life.